The present invention relates to improved hot melt sealants, or more particularly to hot melt adhesives useful for bonding a variety of materials, especially polyamides. Hot melt adhesives are themoplastic materials useful as sealing and bonding agents. At room temperature, they are non-tacky solids but upon being heated they soften or melt into a liquid or semi-liquid tacky condition. The melted or softened adhesive can then be applied to a surface and permitted to cool. The adhesive adheres to the surface. Such a material can thus be used as a bonding agent to join two surfaces, with the adhesive forming an intermediate layer bound to both.
At room temperature the hot-melt adhesives are generally hard, and a thin film of these adhesives has sufficient tensile strength and elongation so that in many cases it is stronger than the surface being bonded. The adhesives are generally insensitive to pressure once permitted to cool to their solid state. Hot melt adhesives are advantageous due to their low cost, solid nature, quick setting time and ease of handling. As a result of these advantages they have been widely used in the fields of packaging, metal and woodworking. Many types of hot melt adhesives are well known to the skilled artisan. Most commonly, hot melt adhesives comprise a polymer such as ethylenevinyl acetate copolymer (EVA), ethylene-acrylate copolymer and other ethylene copolymers, polyethylene, thermoplastic rubber, polyamide, polyurethane, polyester and similar thermoplastic high-molecular-weight polymers. They frequently also contain a tackifying resin, and a viscosity-controlling agent such as various kinds of waxes. Useful tackifying resins include natural resins such as rosin resin and terpene resin and petroleum resins.
One problem with hot melt adhesives compositions is that they are not universally good adhesives for all materials. For example, some are good bonding agents for paper, glass and wood, but not for metals and plastics. Many adhesives are formulated for their holding properties to specific plastics. This is a function of the type of bond which may be formed by the chemical nature of the adhesive and the materials to be joined. In this regard, many hot melt adhesives are known in the art. U.S. Pat. No. 3,929,938 teaches a mixture of a copolymer of ethylene with a vinyl ester or acrylic ester of a saturated alcohol, and a limonene/phenol condensation product. U.S. Pat. No. 3,991,025 describes a polymerized urethane elastomer, a tackifying resin, a plasticizer, an adhesion promoter and an inert filler. U.S. Pat. 3,931,077 teaches a reactive urethane prepolymer, thermoplastic polymer such as an ethylene-vinyl acetate copolymer and a tackifier. U.S. Pat. No. 3,449,273 teaches a hot melt adhesive which is a mixture of a polymeric fatty acid polyamide and a hydroxyphenolic compound. U.S. Pat. No. 3,408,253 relates to a bonding cement which is an ethylene-propylene-polyene terpolymer rubber. U.S. Pat. No. 3,586,738 claims an adhesive which is heat hardenable and has a chlorine containing elastomer copolymerized with chloroprene. U.S. Pat. No. 3,944,523 discloses poly (phenol/diene) copolymer resins blended with rubbery polymers to produce adhesive compositions having improved tack. U.S. Pat. No. 3,976,606 relates to tackified adhesives containing a terpene-phenolic resin. U.S. Pat. No. 4,032,486 relates to an adhesive tackified with a phenol-diene-olefin resinous reaction product. U.S. Pat. No. 4,127,545 relates to a hot melt sealant comprising a butyl rubber, an ethylene-vinyl acetate copolymer and a phenolic resin. U.S. Pat. No. 4,618,640 teaches a hot melt adhesive comprising an ethylene-vinyl acetate copolymer, a wax and a tackifying resin. U.S. Pat. No. 4,284,541 relates to pressure sensitive hot melt adhesives compound containing a modified ethylene-olefin graft copolymer rubber. U.S. Pat. No. 2,307,885 teaches a lubricating composition containing a vinyl phenol polymer and a vinyl acetate. U.S. Pat. No. 3,448,178 provides a hot melt adhesive containing an ethylene/vinyl acetate copolymer and a phenolic modified terpene resin. U.S. Pat. No. 3,790,647 relates to an ethylene propylene diene rubber with an alkyl substituted phenol acetylene resin. U.S. Pat. No. 2,861,002 provides a hot melt adhesive of a polyvinyl acetate and a plasticizer. U.S. Pat. No. 4,324,871 teaches a hot melt adhesive composition containing an ethylene-vinyl acetate copolymer, an alkenyl succinic anhydride and a tackifying resin. U.S. Pat. No. 4,338,414 discloses an adhesive of an ethylene copolymer, polystyrene resin and alkenyl succinic anhydride. U.S. Pat. No. 4,412,030 shows a hot melt adhesive comprising a styrene/phenolic resin and a modified ethylene vinyl acetate copolymer. U.S. Pat. 3,886,234 provides an adhesive resin composition comprising an ethylene-vinyl acetate copolymer, an unsaturated carboxylic acid, an organic peroxide and an optional phenol. U.S. Pat. No. 4,131,709 provides adhesive compositions with a block copolymer of elastomeric and a non-elastomeric members plus an alkylphenol aldehyde resin. U.S. Pat. No. 4,460,728 relates to a hot melt adhesive containing a copolymer of ethylene and vinyl acetate, atactic polypropylene, tackifying resin, plasticizing oil, petroleum wax and a stabilizer. U.S. Pat. No. 4,148,775 describes a hot melt adhesive of a polyamide copolymer resin and a terpene-phenol resin.
The present invention provides an improved hot melt adhesive composition which includes as a component a homopolymer or copolymer of poly (p-hydroxystyrene). Such adhesives demonstrate improved adhesion to polyamides which is believed to be the result of covalent bonds formed by hydroxyl groups with the polyamide.